Midterm Exam Solutions for General Physics I | PHYSICS 140, Exams of Physics

Download Midterm Exam Solutions for General Physics I | PHYSICS 140 and more Exams Physics in PDF only on Docsity!

Physics 140, Fall

FirstMidtermExam

Physics Department, University of Michigan

October 4, 2012 FORM 1

5OLUT1O

Please print yourname:

Your INSTRUCTOR:___________________

INSTRUCTIONSANDINFORMATION

1. Fill in YOUR NAME, UM ID NUMBER, and the EXAM FORM NUMBER on the scantron.
2. RECORD YOUR ANSWERS ON THE SCANTRON USING A #2 PENCIL.
3. Turn in this exam copy with your scantron answer sheet.
4. This is a 90-minute, closed book exam. You may use one 3” x

5” card on which you have your

favorite equations. You also may use a calculator but please do not share calculators.

All cell phones and other communication devices must be shut off and out of sight.

There are

altogether 20 multiple choice questions. All questions are of equal value and

there is

no penalty for guessing.

Equations/values that you may find useful:

x = x 0

• vot

½ at 2

v=V 0 )( + at

arad =v 2 /r

F = ma

Fk = llkN

g = 9.8mIs 2

Physics 140, Fall 2012, Midterm I

Problem 1:

The following operation with unit vectors (i x

(jx

1. yields

A. k C.1 D.

A A

i\

C

X

— -

-L -II

I’

Problem 2:

The figure shows the velocity versus time graph for a ball. Which explanation best

fits the motion of the ball as shown by the graph?

A. The ball is falling, is caught, and is thrown down with greater velocity.

B. The ball is rolling, stops, and then continues rolling. v

The ball is

rising, hits the ceiling, and falls down.

D. The ball is falling, hits the floor, and bounces up.

t

E. The ball is rising, is caught, and then is thrown down

with greater velocity.

ite

r

‘e

dci

r

(dew

cJ

Problem 3:

Physics 140,Fall2012,Midterm 1

A dolphin jumps with an initial velocity of 25 mIs at an angle of

300

above the

horizontal. The dolphin passes through the center ofa hoop beforereturning tothe

water. Ifthedolphinismoving horizontallyatthe instant itgoesthrough the hoop, how

high,H,above thewateristhe center of the hoop?

A. 4.8m B.6.3m

l’e

tk

/1OLAJI

Problem 4:

D.12.5m E.16.0 m

= V —21I

0

5(3D)1— 19.-H

Abody moves along thexaxis. The xcomponent ofitsvelocityas afunction oftime

isknown:v(t) =at 2 — bt 3 ,wherea = 6 mIs 3 andb= 4 mIs 4. If the body is

at the

originat I=0,what will the x coordinate of the body’s positionbeat t=2 s?

C.3m D.4m E.6m

cLC&)

at

=(c

0

2

—

C

0

Physics140,Fall2012,Midterm 1

Problem5:

Three boxes with masses1fl = 1 kg, rn2= 2 kg, and 1fl3 = 3 kg are hanging from

stringsas showninfigure. You arepulling the top string with the forceof 100 N.

What isthetensionT 12 inthe string connecting 1 kg

and 2 kg boxes?

A.20N

‘)F

=

B.49N

‘ 0

LT 1 (1*m 3 ) 8

=

C. 59N

—

(9nIimL1, 3 )4 4 lL)

D. 72 N

—

j]

• —

.

3

‘‘

Problem6:

Hector and Achilles compete with each other introm ofthe gatesof Troyin a

game

of tug-of-war. The twoheroes stand on opposite sidesof amud puddle andattempt

to pull the other into the mud. Eventually, Hector pulls Achilles into the puddle.

Which ofthe following is an accurate description of the reasons behind Hector’s

victory?

A. We really do not know why Hectorwins since from the information given, we do not

know which of the two heroes exertsalarger force on the

other.

B.

Hector and Achilles both exert the same force on the rope. Hector wins because the rope

exertsagreater force on Achilles thanitexerts on Hector.

C.

The

rope exerts the same force on Hector that Hector exertson the rope. The rope also

exerts the same force on Achilles that Achilles exerts on the rope. Hector wins because

the force that he exerts on the ropeis greater than the force that Achilles exerts on the

rope.

Hector and Achilles both exert the same force on the rope and the rope exerts the same

force on both heroes. Hector wins because he exerts agreater frictional force on the

ground than does Achilles.

IL

E. Hector wins because his

victory was ordained by Zeus.

Problem7:

Physics 140,Fall 2012,Midterm 1

You aretaking an Amtrak train from Ann Arbor toChicago. Thereare several

track segmentsinMichigan where trainsrunatsteady 110 milesper hour,andyour

trainisononeofthese segments. Your little cousinhangs atoy onastring attached

to theluggage shelf above yourseats. ifthetrainisroundingacurve to

the right,

whatisthecorrect forcediagramfor forces acting on the toywhile onthatcurve?

Problem8:

A child rides on the rim of a merry-go-round moving in uniform motion with a

period of 5 s and with a

magnitude of acceleration of6.3mIs 2 .The childdropsa

piece of candyjust atedge of the rim aheight 1.2 m above the ground. What

horizontal distance does thecandy travel before hittingthe ground?

A. B. 4.6 m C.5.Om D.7.2m E.8.7m

T

--

I

A C D E

Z6”

‘ —‘

r

7

2711)

ftc—

)V—

T

T

ka*

0”

tke x-axi’s :

=

v-1:

(up.

n&oi1’d)1)

Opi

j..c*.)L(& :

0

=

Hto—±l

(ftt +u1)

W

&Dtve

f

t44e

c 4 J

v

N

724P

=

Ut

tLte

__

. /ZL

Lf

7r

\ 9.

Physics [40, Fall 2012, Midterm 1

Problem 9:

Figure shows a 10 kg mass suspended from two springs scales,

each of which has

negligible weight. Thus,

A. Each scale will read 5 kg.

B. The

top scale will read zero, the lower scale will read 10 kg.

C. The lower scale will read zero,

the top scale

will read 10 kg.

D. Each scale

will read between 1 kg and 10 kg, such that the two add to 10

kg.

[i None of the above.

(C

,\FJtd

4ok

i-

, —

Cia

nko,I1)

-6tJt*)iJ

(eF).

Problem 10:

A river flows due south with a speed of 1.5 mIs. A man

steers a motorboat across

the river; his velocity relative

to the

water is 6 mIs due east. The river is 480 m

wide. How

far south of

his starting point will he reach the opposite bank?

TAj

ml

B. 150 m

C. 225 m D. 240 m K 300 m

x

= Vswt

y:V

ç

I

c.

1

(-)

4.)

Physics140, Fall2012,Midterm I

Problem11:

Each of the three diagrams at right shows consecutive positions of an object

(circles) aswellasvectorsofits velocity (arrows) atmoments separatedbyequal

time intervals. Inthe order of appearance ofthediagrams, thetotal force acting on

theobjectineachsituation ispointing...

A. down, down, down

B. down,up,left

C. zero, down, right

zero, up,down

E. zero, zero, left

Problem12:

A mass mj onatableisattached byamassless stringto asecond mass m

hanging

fromapulleyasshown. The pulley ismassless and frictionless. The tablehasa

rough surfacesothereis a frictional force onmass lflj. Massin 1 isobservedto be

sliding sideways ataconstantspeed. Whatisthe magnitude ofthe frictional force?

Neglect any airresistance.

constant peed

A. ing

LL

m2g]

C. (m2-lnl)g

D.

(rn

+ni)g

E.

(nl

—

ml)g/(1n

f

Xi’s

T—

tS:

p,Dr)1ICo)o

F,

jFr..i

Fzo

I

I

0

/

‘

ce

cIQ’- S

—

I

,c:

))12.

T=,I.

Physics 140,Fall2012, Midterm I

Problem13:

Anobject ofmassinsits ona

bathroom scale placedon the floorofanelevator.

The elevatorisgoingdownandisslowing downwithaconstant acceleration of

magnitude a. Whatisthereadingofthe bathroomscale’?

‘s2w

---

—

L=

1S

4 4ftoi

t:

0

-r

3m

in

flj

3m

A. ma

B. ing

C. m(cl-g)

D.

in(g

• a)

E. ,n(a +g)

1

moving

downward

andslowing

---

PAJ

ppJ

we*t).

Problem14:

An Atwood’s Machine consists of

two blocks suspended over amassless,

frictionless pulley withamassless string. The blocks have massesmand3m, as

shown. Whatisthemagnitude ofthetensionin thestring’?

A. mg 2

B. 4mg/

C.

2mg

[D. 3mg/

E. 3mg

3M r_3=3n(a)

:

• nil ()

/

2 (3ii)

i)

‘2i

3)i

(

‘

3

1M46 ,

L

cL-

UAAdi/-

tt

0 L

S

Or,

tZ4. k-

frr

L DLLQkf’tA-d

)4-

x

rob1ern16:’

4

(5-1)

÷)(ç_

-!.

An object ismoving clockwise aroundan oval-shapedtrack. Itsacceleration vector,

whichisalwaysatright anglestothetrajectory,is shown whentheobjectisatthree

different positions, labeled1,2,and

3. ‘Whichstatement best describesthemotion

oftheobject’?

A. The object moves withadecreasing speed

The object moves with aconstant speed

C. The object moves with anincreasing speed

D. The object moves with constant velocity

E. None ofthe above

(

— >

cJ c

• i

J

cJ-€

t’i

/V,p&ø

,,‘

1&C

(,eS(

CLk

(vda) Ct&t i

Physics 140, Fall2012,Midterm 1

Problem15:

Anobject moves alongthex-axis with thevelocity showninthe graph. Whatisthe

magnitude ofthe displacement ofthe object between times of 2 sand 5 s?

0.5 m

1.0m

A.

B.

1.5m

I). 2.Om

E. 2.5rn

vx

A

L —

=—16 fAl= 4 S

t

N

2-

A /2rr€41(

b-

t&’ afrele,.j

&=_

1,/? ek)e4-.

2-s

cw

a&d

ti’- 44

L4&&

I

e

tro, ‘I

I,

a

IlL

1

W1f

ai tZ

IA4& &

)14.aw

7’7’.t’(-?

Physics 140, Fall 2012, Midterm I

Problem 17:

A river is flowing south with speed 6 km/h with respect to the shore. A barge is

steaming north with speed 10 km/h with respect to the river. A dog is running

east

on the barge’s upper deck with speed 8 km/h with respect to the barge. What is the

speed of the dog with respect to the shore?

A. 8 km/h m/h C. 10 km/h D. 13 km/h E. 18 km/h

V

÷

--

V 1 s

=

--

(V 8 g

—Vg)

\j

S [

• (to-

Problem 18:

Two blocks, a big block of mass 3M and a little block of mass M,

are both being

pushed along a surface by a

horizontal external force of magnitude F, as shown.

There is friction between each of the blocks and the table but not between the two

blocks. Both blocks are made of the same material. The blocks are moving to the

right and speeding up. What is the magnitude of the normal force, which the

big

block exerts on the little block?

‘1’

A. F

B. Ff

€ t&.

C.F/

D. 2F/

G.

E.3F

M

tA. 41

=

T +D

-

t%

—*

-

/k

F

F

&

‘

Ma

A!

__

Problem 19:

Physics 140, Fall 2012, Midterm I

What is the angle

between vectors A = — 3 i + 4 j

and B = I

— 2j + 2

k?

D. 133°

A

By

÷

/4A1A.

(_3)(4)

-fr

(4)(_:2.).f

(o’)(2_)

—

— %

÷ 0

I’

• Ic

=)

isj

i?1-.17-

Problem 20:

The picture below shows an upper block of mass mA

and a lower block of

mass flip

connected by a

light string wrapped around

a massless and frictionless pulley. The

coefficient of kinetic friction between the blocks and between the block B and the

table is

Ilk.

For the blocks to move at constant speed what force F

must you apply?

A. p(rn 4 +mjg

B.

Ilk

(2mA

• m )g

C.

Pk(”’A

+2,njg

E{

p(3in, 1 +m)g

E.

Ilk

(in, 1 +

3 mB

)g

x

T—FfBA

y

Fg 4

—

+AQ

—F

FAB

z 1 L F,. 146

4

(A

A.

43° B. 47° C. 71°

Ps

=

fl1Aj

T

7

-f-,,Lt c

+W6) 4

t/

WWJ

V

11g